1. Field of the Invention
Exemplary embodiments of the present invention relate to packet mode auto-detection in a multi-mode wireless communication system, signal field transmission for the packet mode auto-detection, and gain control based on the packet mode; and, more particularly, to a method for automatically detecting a packet mode in a multi-mode wireless communication system (e.g., a Wireless Local Area Network (WLAN) communication system supporting various modes) by using a data rate value and a packet length setting value, a method for transmitting a signal field for auto-detection of a packet mode by phase rotation of a data tone and/or a pilot tone at the signal field transmission, and a method for performing an automatic gain control according to the detected packet mode.
2. Description of Related Art
In general, a wireless communication device based on the IEEE 802.11n standards uses up to four multiple antennas and a 40 MHz bandwidth and reduces an overhead, thereby making it possible to transmit data at a data rate 10 times higher than a 54 Mbps data rate of a wireless communication device based on the conventional IEEE 802.11a/g standards. Hereinafter, a wireless transmission mode based on the IEEE 802.11a/g standards will be called a legacy mode, and a wireless transmission mode based on the IEEE 802.11n standards will be called a High Throughput (HT) mode.
An HT signal field HT-SIG is added in an IEEE 802.11n packet in order to maintain the compatibility with a legacy mode such as IEEE 802.11a/g while supporting an HT mode of IEEE 802.11n. The addition of the HT signal field in the IEEE 802.11n packet is to facilitate the discrimination from a legacy packet and to process a received signal in conformity with the HT packet frame format.
In general, a legacy transmission frame includes an Orthogonal Frequency Division Multiplexing (OFDM) packet preamble, a signal field, and an OFDM data field. For compatibility with the conventional IEEE 802.11a/g standards, an IEEE 802.11n-based transmission frame includes: a common part receivable by both a legacy terminal and a HT terminal; and a HT-dedicated part receivable only by an HT terminal. The common part includes an OFDM packet preamble (L-STF, L-LTF) and an L_SIG field that is a signal field for a legacy terminal. The HT-dedicated part includes an HT-SIG1/HT-SIG2 field (i.e., a signal field for an HT terminal), an HT-SIF/HT-LTF field (i.e., a preamble field for an HT terminal), and an OFDM data field.
In such an HT transmission frame structure, a discrimination between a legacy mode and an HT mode is made between L-SIG and HT-SIG. For a discrimination between a legacy mode and an HT mode, a conventional method transmits an HT signal field by modulating it by a Quadrature Binary Phase Shift Keying (Q-BPSK) scheme that rotates the phase of a data tone of the HT signal field by 90 degrees, as illustrated in FIG. 1.
That is, as illustrated in FIG. 1, an HT signal field HT-SIG is transmitted by 90 degree phase modulating a data tone of the HT signal field HT-SIG in comparison with a legacy signal field L-SIG. Thus, a receiving (RX) terminal can determine whether an HT signal field HT-SIG or a data field for a legacy terminal is received after a legacy signal field.
However, such a conventional packet mode detection method has a great difficulty in discriminating a Q-BPSK modulation signal of an HT signal field and a 64-QAM modulation signal for data. In order to solve such a problem, the conventional method discriminates between a 64-QAM signal and a Q-BPSK signal by comparing the accumulation values of the mapped signal values by using a detection threshold value as illustrated in FIG. 1. However, such a conventional packet mode detection method has the following problems.
First, the conventional method is low in terms of the reliability of packet mode detection. The method of discriminating between a 64-QAM signal and a Q-BPK signal by a detection threshold value as illustrated in FIG. 1 is low in terms of a signal-to-noise ratio (SNR) and has a high probability that a mode detection error may occur due to a noise in a poor environment with a severe channel change. A 64-QAM signal is the maximum modulation mode in the conventional method, but the problem becomes more serious if the higher modulation scheme (e.g., a 256-QAM modulation scheme) is used for a very high throughput mode. Therefore, a simple comparison of BPSK and Q-BPSK can be made according to the 6 Mbps data rate setting of a legacy signal field, but it is difficult to detect an error in the legacy signal field through a one-bit parity check if a channel environment is poor.
Secondly, the conventional method is low in terms of extendibility. If the conventional method is used to discriminate between an HT mode and a Very High Throughput (VHT) mode (the mode following the HT mode) in the HT-SIG, an automatic packet mode detection becomes impossible because the I energy and the Q energy become equal in the case of a terminal using both of the two HT-SIG symbols among the terminals supporting the IEEE 802.11n standards. Accordingly, the total network throughput decreases and the power consumption efficiency decreases.
The above problems of the conventional method may become more serious when detecting packets based on the Very High Throughput (VHT) wireless communication standards (e.g., IEEE 802.11ac) following the conventional wireless LAN standards. Hereinafter, the IEEE 802.11ac-based wireless transmission mode will be referred to as a VHT mode.